fix neutrino mass parameter in camb

[liuxx479]

Originally, omega_cdm (omch2) assumes all matter in cold dark matter and baryons, and ignores massive neutrinos:
omch2=(self.cosmo.Om0 - self.cosmo.Ob0) * self.cosmo.h ** 2

I changed the definition to include massive neutrinos:
omch2=(self.cosmo.Om0 - self.cosmo.Ob0 **- self.cosmo.Onu0**) * self.cosmo.h ** 2
where I used astropy's cosmo.Onu0 calculation.

In addition, camb requires the neutrino mass and hierarchy.. I did not fix the code for different hierarchies (normal, inverted, degenerate) since it should be a sub-percent effect that's not observable by near future LSS surveys. So I assumed degenerate hierarchy (i.e. the 3 neutrinos are assumed to have equal mass = 1/3 *total mass):

mnu=sum(self.cosmo.m_nu.value)
neutrino_hierarchy='degenerate'

[codecov]

Codecov Report

Merging #118 (8b24f5d) into dev (cb19a62) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev     #118   +/-   ##
=======================================
  Coverage   85.68%   85.68%           
=======================================
  Files          26       26           
  Lines        2285     2285           
=======================================
  Hits         1958     1958           
  Misses        327      327           

Impacted Files	Coverage Δ
src/hmf/density_field/transfer_models.py	87.79% <ø> (ø)

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[steven-murray]

Thanks @liuxx479, this is much appreciated. Can I get you to do three things:

First, do pre-commit install in the top-level directory (this will catch the linting problems before a commit is checked in). If you don't have pre-commit you can first do pip install pre-commit.

Secondly, add this change to the CHANGELOG.rst under dev-version (or make that sub-heading if it doesn't exist), under Fixes.

Thirdly, add your name to the contributors list!